The invention relates to a method of manufacturing an aspherical optical element. The aspherical optical element includes a substrate having an approximately spherical surface and a synthetic resin correction layer provided on the spherical surface. The free surface of the correction layer is convex aspherical and has a collection of inflection points situated approximately on a circle.
According to the method, the substrate is placed opposite to and spaced from a rotationally symmetrical matrix which has a concave aspherical surface having a collection of inflection points situated approximately on a circle. A curable liquid synthetic resin composition is provided between the matrix and the substrate, and the distance between the matrix and the substrate is reduced to a desired final position. The synthetic resin composition is then cured, and the substrate together with the correction layer connected thereto are removed from the matrix.
The invention also relates to a device for performing the method, and the aspherical optical element made by the method.
The method may be used, for example, for manufacturing monaspherical lenses.
British patent 1,301,551 discloses a method of manufacturing an aspherical optical element by providing a thermosetting layer of synthetic resin on a flat or spherical substrate, for example for correction of aberration. The variation in thickness of the layer of synthetic resin must be in agreement with the desired correction. A positive curvature may be necessary in the center of the optical element and a negative curvature may be necessary at the edge. In between, a collection of inflection points exists on the surface of the correction layer.
If the layer of synthetic resin is too thick, inaccuracies arise due to shrinkage of the resin during curing. The correction layer may be made thinner by providing the substrate with approximately the desired surface, but a spherical substrate can be manufactured more simply and more accurately than a substrte having an aspherical surface.
When a spherical substrate is used it is necessary to center the substrate accurately with respect to the matrix prior to curing the synthetic resin. For that purpose, a guiding mechanism may be provided to keep the matrix and the substrate in their desired positions.
A thermosetting resin is used in the method described in British patent 1,301,551. Alternatively, the synthetic resin may be light-curable, as described, for example, in German patent application 2,637,257 (corresponding to British patent 1,535,986).